An internal combustion engine as set out above is described in the Applicants' earlier GB Patent Application No. 0708967.5. In the accompanying drawings, FIG. 1a is a perspective view of a valve actuating mechanism as described in the latter patent application and FIG. 1b is a section through the same mechanism. A poppet valve 10 is urged towards its closed position against its valve seat in the engine cylinder head by a valve spring 12. A downwards force to open the valve 10 is applied by an actuating rocker 14 of which the opposite end is pivoted on an adjustable articulated link 16. Valve actuation is effected by a camshaft driven in synchronism with the engine crankshaft which carries two cams 20 and 22 that can be phase shifted in relation to one another. The cam 20 is formed from two identical parts that straddle the other cam 22. A summation lever 24, which is pivotably carried by the actuating rocker 14 has roller followers 26, 27 at its opposite ends one of which is maintained in contact with a respective one of the two cams 20 and 22 by a control spring 28. The control spring 28 is required in a cam summation system of this type in order to control the motion of the summation lever 24 and to maintain contact between the actuating rocker 14 and the valve tip whilst the valve is closed. It can be seen from FIG. 1b that the control spring 28 acts in a downward direction to force the adjacent cam follower 26 away from its cam lobe 22, and this forces the two followers 27 on the opposite side of the summation lever into contact with their respective cam lobes 20.
The present invention seeks to provide an improvement of the valve actuating mechanism described above which additionally enables the valve 10 to be deactivated.
It has been previously proposed in WO03/016684 to provide valve deactivation in a valve train employing a summation lever by forming the summation lever in two parts that may be selectively locked to one another. FIGS. 2a, 2b and 2c of the accompanying drawings correspond respectively to FIGS. 11, 12 and 13 of WO03/016684. The two parts 24a and 24b of the summation lever are pivotable relative to one another about a pivot pin 30 and can be locked to one another by a locking pin 32. In the locked position shown in FIGS. 2a and 2c the summation lever moves as one piece and opens the valve 10 under the action of the two cams 20 and 22. However, when the locking pin 32 is released, as shown in FIG. 2b, the two parts 24a and 24b are merely articulated relative to another by the action of the two cams 20 and 22 and the valve remains closed.
It is well accepted that a valve deactivation system requires a lost motion spring to control the position of the valve train system and maintain contact between each cam lobe and its follower during the cam lift event when it is being operated with the valve deactivated. However, WO03/016684 is silent on how such a spring is incorporated in the valve deactivation system.